In general there are no essential subjects that you must take at A-level (or equivalent) to become a lawyer.
However, to demonstrate that you have the skills, you may want to choose subjects that involve research, analysis and communication - such as history, geography, modern languages, sciences or maths - as these can give you an edge. Be aware that many universities do not accept general studies or critical thinking A-levels.
Legal work is intellectually challenging and competitive, so universities expect excellent A-level grades as evidence that you'll be able to cope with the demands of studying law.
As such, entry requirements for an undergraduate law degree at top universities typically range from A*AA to AAB. Other institutions will have less stringent criteria so check when searching for courses.
Some universities will specify required GCSE grades in English, maths and possibly a foreign language.
In addition, to study law at university you will often have to take the National Admissions Test for Law (LNAT) as part of your application. This does not test your knowledge of law - instead, it assesses your aptitude for the required skills.